1. Field of the Invention
The present invention relates to an alignment unit and an exposure apparatus.
2. Description of the Related Art
For an alignment used for an exposure apparatus, Japanese Patent Laid-Open Nos. (“JPs”) 2-142110 and 5-36583 propose to accord a value of a weighted average of coordinates of alignment marks formed on a layer that is located under a target layer on a substrate, with a coordinate of an alignment mark on the target layer. JP 7-263332 proposes, in measuring a position of an alignment mark on each layer, to add a calculated offset value to the position of the alignment mark. JP 7-321012 proposes a method for using a value of a weighted average as a reference position to expose a pattern of a next upper layer, which weighted average is made with a weight that includes a measurement error in measuring a position of an alignment mark formed on a first layer on a substrate and a necessary alignment precision of each layer. Other prior art include JPs 2000-21766, 9-218714, and 2-294015.
However, none of JPs. 2-142110, 5-36583, 7-263332, and 7-321012 discloses a concrete value of the weight. It is conceivable to determine the weight in accordance with the relevancy to the pattern of the original. Nevertheless, when the pattern of the lowermost layer in which the pattern generally has a minimum critical dimension (“CD”) is less relevant to the pattern of the original, a positional shift amount increases problematically between a pattern of an uppermost layer and a pattern of the lowermost layer. It is also conceivable to determine a weight through a simulation but this method is arduous.